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United States Patent |
6,066,771
|
Floyd
,   et al.
|
May 23, 2000
|
Smelting of carbon-containing material
Abstract
A process for treating carbon-containing material contaminated with toxic
elements utilises smelting of the material in a top-submerged lancing
reactor. The material has its carbon content present as elemental or free
carbon. Smelting is conducted so as to form, or in the presence of, a
fluid slag. In the course of smelting, free-oxygen-containing gas is
injected into the slag by top-submerged injection, to combust the carbon
content of the material. Volatilizable toxic elements are discharged in
reactor off-gas, while non-volatilizable elements are substantially fully
incorporated into the slag.
Inventors:
|
Floyd; John M (Upper Beaconsfield, AU);
Jeppe; Carl P (Shoreham, AU);
Matusewicz; Robert W (West Footscray, AU);
Robilliard; Kenneth R (Upwey, AU)
|
Assignee:
|
Ausmelt Limited (Dandenong, AU)
|
Appl. No.:
|
832118 |
Filed:
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April 3, 1997 |
Foreign Application Priority Data
Current U.S. Class: |
588/314; 110/341; 423/DIG.12; 431/2; 588/405; 588/410 |
Intern'l Class: |
A62D 003/00 |
Field of Search: |
588/1,201,205,213,228
423/DIG. 12
75/10.29,10.3,10.4,10.46,10.59
110/341
431/2
|
References Cited
U.S. Patent Documents
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2848473 | Aug., 1958 | Rummel | 260/449.
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3527178 | Sep., 1970 | Southwick | 110/8.
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3647358 | Mar., 1972 | Greenberg | 23/2.
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3668120 | Jun., 1972 | Patterson | 210/60.
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3706549 | Dec., 1972 | Knuppel | 75/60.
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3744438 | Jul., 1973 | Southwick | 110/8.
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3812620 | May., 1974 | Titus | 48/65.
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3845190 | Oct., 1974 | Yosim.
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3890908 | Jun., 1975 | Von Klenck | 110/8.
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3974784 | Aug., 1976 | Greenberg | 110/8.
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4043766 | Aug., 1977 | Gernhardt | 48/73.
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4140066 | Feb., 1979 | Rathjen | 110/235.
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4145396 | Mar., 1979 | Grantham | 423/22.
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4230053 | Oct., 1980 | Deardorff | 110/346.
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4244180 | Jan., 1981 | Rasor | 60/39.
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4246253 | Jan., 1981 | Grantham | 423/659.
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4346661 | Aug., 1982 | Nakamura | 110/259.
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4388084 | Jun., 1983 | Okane | 48/197.
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4389246 | Jun., 1983 | Okamura | 75/60.
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4400936 | Aug., 1983 | Evans | 60/274.
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4402274 | Sep., 1983 | Meenan | 110/346.
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4431612 | Feb., 1984 | Bell | 422/186.
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4432344 | Feb., 1984 | Bennington | 126/438.
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4447262 | May., 1984 | Gay | 75/65.
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4481891 | Nov., 1984 | Takeshita | 110/238.
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4574714 | Mar., 1986 | Bach | 110/346.
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4602574 | Jul., 1986 | Bach | 110/346.
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4735784 | Apr., 1988 | Davis | 423/111.
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4763585 | Aug., 1988 | Williams et al. | 110/346.
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5000101 | Mar., 1991 | Wagner | 110/346.
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5177304 | Jan., 1993 | Nagel | 588/201.
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5191154 | Mar., 1993 | Nagel | 588/201.
|
5251879 | Oct., 1993 | Floyd | 266/44.
|
5271341 | Dec., 1993 | Wagner | 110/346.
|
5277846 | Jan., 1994 | Tanari.
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5282881 | Feb., 1994 | Baldock | 75/500.
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5298233 | Mar., 1994 | Nagel | 423/580.
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5301620 | Apr., 1994 | Nagel | 110/346.
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5304701 | Apr., 1994 | Igarashi | 588/201.
|
5308043 | May., 1994 | Floyd | 266/78.
|
5322547 | Jun., 1994 | Nagel | 75/414.
|
5395405 | Mar., 1995 | Nagel | 48/197.
|
5396850 | Mar., 1995 | Conochie | 110/346.
|
5449505 | Sep., 1995 | Gay | 423/332.
|
5491279 | Feb., 1996 | Robert et al. | 588/201.
|
Foreign Patent Documents |
1678788 | Dec., 1988 | AU.
| |
7933291 | Jun., 1991 | AU.
| |
0550136 | Jul., 1973 | EP.
| |
0085153 | Aug., 1983 | EP.
| |
0294300 | Dec., 1988 | EP.
| |
0465388 | Jan., 1992 | FR.
| |
2719284 | Nov., 1977 | DE.
| |
58-73742 | May., 1983 | JP.
| |
59-28505 | Feb., 1984 | JP.
| |
59-27117 | Feb., 1984 | JP.
| |
1189883 | Nov., 1985 | SU.
| |
9108023 | Jun., 1991 | WO.
| |
92/01492 | Feb., 1992 | WO.
| |
93/10862 | Jun., 1993 | WO.
| |
Other References
Slag Atlas, Dusseldorf, Verlag Stahleisen M.B.H., 1981, pp. 194, 195 and
199.
Rosenquist, T., Principles of Extractive Metalurgy, McGraw-Hill, 1974, pp.
340-341.
Database WPI, Section CH, Week 8622, Derwent Publications Ltd., London, GB;
Class M24, AN 86-143075 X P002022173 & SU-A-1 189 883 (Zhdanov Metal
Inst), Nov. 7, 1985 Abstract.
|
Primary Examiner: Mai; Ngoclan
Attorney, Agent or Firm: Ladas & Parry
Parent Case Text
This application is a continuation of application Ser. No. 08/532,710 filed
on Feb. 7, 1996 now abandoned, which is a 371 of International Application
PCT/AU94/00159 filed on Apr. 5, 1994 and which designated the U.S.
Claims
We claim:
1. A process for treating carbon-containing material contaminated with
toxic elements, in which the carbon is present essentially as free or
elemental carbon in a solid, particulate or lump form wherein the process
comprises the steps of:
(a) charging the carbon-containing material to a top-submerged lancing
reactor and smelting the carbon-containing material in said reactor in the
presence of a fluid slag,
(b) directly injecting an oxygen-containing gas into the slag during the
smelting, by a top-submerged lance, to combust substantially all of the
carbon content of the carbon-containing material, and
(c) discharging volatilizable toxic elements as fume in reactor off-gas and
substantially fully incorporating non-volatilizable toxic elements in the
slag;
wherein the slag is a silica slag containing iron oxide with the iron oxide
present in the slag at a level such that the iron oxide acts as an oxygen
carrier enhancing combustion of the content of the carbon-containing
material by the reactions:
2FeO.sub.(slag) +1/2O.sub.2 =2FeO.sub.1.5(slag) ( 1)
2FeO.sub.1.5(slag) +C=2FeO.sub.(slag) +CO (2)
and maintaining these reactions by turbulence in the slag generated by the
top-submerged injection of the oxygen-containing gas.
2. A process according to claim 1 wherein a suitable flux material is added
to the carbon-containing material to form the fluid slag.
3. A process for treating carbon-containing material contaminated with
toxic elements, in which the carbon is present essentially as free or
elemental carbon in a solid, particulate or lump form; wherein the process
comprises the steps of:
(a) charging the carbon-containing material to a top-submerged lancing
reactor and smelting the carbon-containing material in said reactor in the
presence of a fluid slag,
(b) directly injecting an oxygen-containing gas into the slag during the
smelting, by a top-submerged lance, to combust substantially all of the
carbon content of the carbon-containing material, and
(c) discharging volatilizable toxic elements as fume in reactor off-gas and
substantially fully incorporating non-volatilizable toxic elements in the
slag;
wherein the process is conducted in two stages in which top-submerged
lances are operable in at least two zones whereby there is at least one
first zone to which the carbon-containing material is fed and in which its
carbon-content is combusted in a first stage by the top-submerged
injection of oxygen-containing gas and at least one second zone to which
there is no feed of the carbon-containing material and in which mixing and
flushing of slag from the first zone is effected in a second stage by the
top submerged injection of oxygen-containing gas.
4. A process for treating carbon-containing material contaminated with
toxic elements, in which the carbon is present essentially as free or
elemental carbon in a solid, particulate or lump form; wherein the process
comprises the steps of:
(a) charging the carbon-containing material to a top-submerged lancing
reactor and smelting the carbon-containing material in said reactor in the
presence of a fluid slag,
(b) directly injecting an oxygen-containing gas into the slag during the
smelting, by a top-submerged lance, to combust substantially all of the
carbon content of the carbon-containing material, and
(c) discharging volatilizable toxic elements as fume in reactor off-gas and
substantially fully incorporating non-volatilizable toxic elements in the
slag;
wherein the process is operated in a two-cycle batchwise manner wherein the
carbon-containing material is combusted by the top-submerged injection of
the oxygen-containing as, during a first stage, and the top-submerged
injection of the oxygen-containing as provides flushing of the slag during
a second stage in which there is substantially no feeding of the
carbon-containing material.
5. A process according to claim 1, wherein the carbon-containing material
includes spent pot liner (SPL).
6. A process according to claim 1, wherein the carbon-containing material
is vertical retort residue.
7. A process according to claim 1, wherein the carbon-containing material
comprises waste graphite from a nuclear reactor.
8. A process according to claim 1, wherein the carbon content of the
combustion of the carbon-containing material provides all of the heat
requirements of the process.
9. A process according to claim 1, wherein additional fuel is added to the
reactor to provide for the heat requirements of the process.
10. A process according to claim 1, wherein the carbon-containing materials
includes fluorine-containing toxic material and said fluorine is liberated
from said toxic material through reactions including a hydrogen-containing
compound which is added to said carbon-containing in said reactor.
11. A process according to claim 1, wherein the carbon-containing material
includes toxic elements which are oxidised within the reactor to produce
harmless products.
12. A process according to claim 1, wherein said lance additionally is
adapted to discharge oxygen-containing gas into a reactor space above the
slag to provide oxygen for post-combustion of gases produced by the
smelting of the carbon-containing material.
13. A process for treating carbon-containing material contaminated with
toxic elements, in which the carbon is present essentially as free or
elemental carbon in a solid, particulate or lump form; wherein the process
comprises the steps of:
(a) charging the carbon-containing material to a top-submerged lancing
reactor and smelting the carbon-containing material in said reactor in the
presence of a fluid slag,
(b) directly injecting an oxygen-containing gas into the slag during the
smelting, by a top-submerged lance, to combust substantially all of the
carbon content of the carbon-containing material, and
(c) discharging volatilizable toxic elements as fume in reactor off-gas and
substantially fully incorporating non-volatilizable toxic elements in the
slag; wherein the process is conducted at a temperature of from
1100.degree. C. to 1400.degree. C. and the reactor is water-cooled to form
a lining of solidified slag, said lining protecting refractory containment
material of the reactor, at least in regions of the containment material
prone to wear, from dissolution in the fluid slag.
14. A process according to claim 1, wherein the process is conducted at a
temperature from 1100.degree. C. to 1400.degree. C.
15. A process according to claim 14, wherein the reactor is water-cooled to
form a lining of solidified slag, said lining protecting refractory
containment material of the reactor, at least in regions of the
containment material prone to wear, from dissolution in the fluid slag.
16. A process according to claim 3, wherein the process is conducted at a
temperature from 1100.degree. C. to 1400.degree. C.
17. A process according to claim 4, wherein the process is conducted at a
temperature from 1100.degree. C. to 1400.degree. C.
Description
This invention relates to a process for processing carbon-containing
material contaminated with toxic elements.
The carbon content of the carbon-containing material used in the present
invention substantially is present as free or elemental carbon. Thus, the
carbon content may substantially comprise graphite in its various forms
such as block graphite, or amorphous or microcrystalline graphite such as
coke, carbon black and charcoal. However, the carbon-containing material
additionally can include carbonaceous material such as bituminous
materials heavy oil residues, or the like, particularly where used as a
binder for particulate graphitic material.
The invention has particular relevance to contaminated carbon-containing
material produced in electrolytic smelting of aluminium, such as spent pot
liner (SPL) material, and the following description largely is directed to
the processing of SPL material. However it is to be understood that the
invention also relates to the processing of contaminated carbon-containing
material other than SPL material, whether produced in the electrolytic
smelting of aluminium, or in other industries.
Electrolytic reduction cells or pot lines of electrolytic smelters for
recovery of aluminium metal are lined with carbonaceous material.
Typically the reduction cell lining has an outer, refractory
alumino-silicate shell, and an inner carbonaceous shell. During the life
of reduction cells, the carbonaceous shell of the lining is gradually
destroyed by penetration of materials of the electrolytic bath contained
therein, and by ageing under prevailing temperatures. Ultimately, the
outer shell also becomes contaminated by bath materials. The operating
efficiency of the cells declines as a result of these factors,
necessitating replacement of the carbonaceous shell, or of both the inner
and outer shells. Removed material of the lining, comprising SPL material,
then must either be stock-piled, or processed to provide a residue to be
discarded. The processing can result in recovery of some materials, such
as fluorine as HF, and some recovered materials can be recycled to the
smelting operation or to an antecedent operation. The SPL material can
comprise that recovered from the inner, carbonaceous shell ("Cut 1"), that
recovered from the outer shell ("Cut 2") or a mixture of Cuts 1 and 2.
U.S. Pat. No. 4,735,784 to Davis et al discusses prior art proposals of
U.S. Pat. No. 4,065,551, to Dahl; U.S. Pat. No. 4,113,832, to Bell et al;
U.S. Pat. Nos. 4,158,701 and 4,160,809, both to Anderson et al; and U.S.
Pat. No. 4,362,701, to Kruger et al. Further prior art proposals are
provided in U.S. Pat. No. 4,113,831, to Orth, Jr. et al and U.S. Pat. No.
4,444,740 to Snodgrass et al, although the proposals of the latter two
patents are in a distinct context in relating to aqueous leaching
operations.
In relation to the prior art considered in U.S. Pat. No. 4,7357,84, Davis
et al point out that none of the proposals produces a final waste residue
that is rendered inert to health and environmental risks. The proposals
provide a particulate residue from which remaining contaminants are able
to be leached. Also, the proposals teach directly, or indirectly, a need
to avoid conditions resulting in formation of a slag.
Davis et al proposes a method for treating SPL material, in which the
material is mixed with silica, and the resultant mixture then heated at an
elevated temperature to form a slag. The method necessitates sufficient
added silica in the mixture, and forming the slag in the presence of
water, to provide pyrohydrolysis conditions which result in volatilization
of substantially all fluoride contaminants as HF. Thereafter, the slag is
cooled to produce an insoluble silicate glass-residue containing any
remaining fluoride contaminants in an immobile state.
In the proposal of Davis et al, heating of the mixture of waste material
and silica is to a temperature of 1000.degree. to 1700.degree. C. Where
the waste material is SPL material, the major carbon content thereof is
combusted to provide at least a portion of the process heat requirement.
However, the silica addition is to a level of from 7 to 50% by weight of
the waste material, and a resultant disadvantage of the proposal is that
the quantity of residue can exceed that of the waste material feed. This
disadvantage can apply even with combustion of all of the carbon content
of SPL material. Also, the proposal does not enable the fuel value of the
carbon content to be efficiently utilised.
While the present invention has particular relevance to the processing of
SPL material, it is indicated above that it also can be applied to the
processing of other carbon-containing materials. One important example of
another suitable material comprises residues from vertical retorts, such
as used for distilling zinc from concentrates. Similar materials include
waste graphite crucibles used for metallurgical cupellation containing
recoverable precious metal values, and activated carbon-containing
precious metals and/or toxic metals. In the distillation of zinc from a
vertical retort, the concentrates are mixed with coke, and heated in the
retort. The distillation leaves a residue containing carbon from unreacted
coke, some gangue material from the concentrate, and some zinc residue,
typically with some lead and silver.
Another suitable material for which the present invention is applicable
comprises waste graphite blocks from nuclear reactors. Such waste graphite
blocks, of course, are contaminated by radioactive products and, as a
waste material, they present a major problem of either safe storage or
disposal.
The present invention provides a process for processing carbon-containing
material contaminated with toxic elements, with the process enabling the
fuel value of the carbon content to be efficiently utilised. In the case
of SPL material contaminated at least by fluoride, in particular, the
process obviates the need for added silica although, as indicated herein,
silicon can be present in some carbon-containing material to be processed,
typically as silicate.
In the process of the invention, the carbon-containing material is smelted
in a top-submerged lancing reactor or furnace, utilising top-submerged
injection of free-oxygen-containing gas such as air, oxygen or
oxygen-enriched air. The smelting is conducted to form, or in the presence
of, a fluid slag by addition of a suitable flux material. The
oxygen-containing gas is supplied by top-submerged injection into the slag
for combustion of the carbon content of the carbon-containing material,
with the carbon content thus being utilised as at least part of the fuel
requirement for the process. In the course of the smelting SPL material,
fluorine-containing contaminants in the carbon-containing material are
liberated such as through reactions involving a hydrogen-containing
compound, such as water which may be mixed with the SPL feed or water
vapour generated from the hydrocarbon content of fuels. Other toxic
elements in the carbon-containing material, such as H.sub.2 S and HCN are
oxidised within the reactor, such as by the oxygen content of the
top-blown gas, to produce harmless products such as water vapour, carbon
dioxide and nitrogen gas. Sulphur can be either dissolved in the slag or
oxidised to SO.sub.2 which reports to the flue gas, from which it can be
removed in flue-gas scrubbing operations.
In the case of smelting carbon-containing material comprising residue from
a vertical retort, contaminants comprising zinc and lead, as well as any
precious metals present such as silver, can be fumed and recovered from
off-gases from the furnace. To the extent that they are not driven off as
fume, zinc and lead report in the slag, but generally at an
environmentally acceptable low level.
With carbon-containing material comprising waste graphite blocks from
nuclear reactors, the effect of smelting will depend on the radioactive
contaminants present. Some such contaminants will be driven off as fume
with furnace off-gases, while others will be taken up in the slag. In the
case of contaminants present in off-gases, they are able to be recovered
from the gases such as by use of a fabric filter baghouse through which
the gases are passed. Contaminants reporting in the slag are able to be
encapsulated therein as silicates and/or in solution or the like.
Radioactive material typically is present in waste graphite blocks at
relatively low concentrations, with the quantities recovered from
off-gases being small and thus facilitating further processing for their
safe containment and storage. Similarly, quantities present in the slag
are small, while the volume of slag in which they are recovered is
substantially less than that of the waste graphite block feed so that
containment or storage again is facilitated.
The process of the invention most preferably is conducted in a single
furnace comprising the top-submerged lancing reactor. The process is able
to be conducted as a continuous smelting operation. Alternatively, it can
be conducted on a semi-continuous basis in which, after a suitable
smelting period, the feeding of carbon-containing material is stopped, and
mixing and flushing of the slag is continued by top-submerged injection of
oxygen-containing gas, for an interval sufficient to achieve final
evolution of contaminants with the reactor flue gases.
Where the smelting operation is conducted continuously, slag may be tapped
throughout the operation (at least after a sufficient start-up period), or
at suitable intervals. While a continuous smelting operation may not
result in evolution of contaminants to obtain the very low residual level
possible with semi-continuous operation as described above, continuous
operation can be adapted to achieve a comparable low level. Thus, in a
variant providing continuous smelting operation, the reactor used may have
top-submerged lances operable in at least two zones. In that variant there
is at least one first zone of the reactor to which the carbon-containing
material is fed and in which its carbon-content is combusted by the
top-submerged injected oxygen-containing gas; and at least one second zone
of the reactor to which there is no feed of the carbon-containing
material, and in which mixing and flushing of slag from the first zone is
effected by top-submerged injected oxygen-containing gas. In the variant,
slag preferably is tapped continuously or at intervals at a location near
to a second zone and remote from the or each first zone.
The lance or lances providing top-submerged injection of oxygen-containing
gas are positioned to inject the gas in the slag. The lance also will
preferably have facilities for discharge of an oxygen-containing gas into
the gas space above the bath. This discharge is to ensure complete
oxidation, such as by post-combustion, of gases such as carbon monoxide,
hydrogen or hydrocarbon gases to produce harmless gases such as carbon
dioxide and water vapour.
The carbon-containing material most preferably comprises SPL material. It
may comprise SPL material of Cut 1, Cut 2 or of a mixture of Cuts 1 and 2.
Additionally, it may include other waste material from aluminium smelter
operation, such as carbon-containing spent anode material, spent alumina
from smelter off-gas dry scrubbers, channel and trench cleanings, floor
sweepings and spent smelter roof material. Where necessary, the waste
material is crushed but, in contrast to prior art proposals in general,
the crushed material can be relatively coarse. In general, crushing to -20
mm is sufficient.
Some waste material such as floor sweepings, able to be included with SPL
material, is relatively fine. Such material can be agglomerated, if
required, although the process of the invention does not necessitate this.
Coarse material preferably is added to the reactor via an inlet chute in
an upper region such as the roof, of the reactor. Fine material in the
coarse feed, or added thereto can be partly agglomerated by mixing with
water just before entering the furnace. This lightly agglomerated material
then enters the bath and reacts. The feed system is provided with
facilities to draw any gases produced by the wetting operation into the
furnace to ensure that any toxic gases are completely reacted to harmless
gases. In another variation, fines are able to be injected, such as with
oxygen-containing gas supplied by top-submerged injection into the slag.
Loss of fines with reactor off-gases can be avoided in all of these means
so that very little dust from the feed material enters the flue gases.
The carbon-containing material, such as SPL material, preferably is fed in
a continuous manner to the reactor, although batch-wise or intermittent
feed is possible. During the smelting operation, a slag is present. The
slag, or an initial quantity of slag, can be present at the outset, or
slag can be formed in a start-up phase of the smelting operation.
Preferably, slag and/or slag-forming flux is fed to the reactor during
smelting. The slag and/or flux most preferably is fed continously,
although batch-wise or intermittent feed is possible. Depending on the
form of the slag and/or flux, it may be fed via a chute in an upper region
of the reactor, such as with the carbon-containing feed material, or
through the lance providing top-submerged injection of oxygen.
The slag or slag-forming flux may comprise waste slag from an iron- or
steel-making operation or from a non-ferrous smelting operation, iron ore,
basalt, limestone or similar material. The smelting operation of the
process of the invention preferably is conducted at a temperature of from
about 1100.degree. C. to about 1400.degree. C. The slag or slag-forming
flux most preferably is such as to provide a suitably fluid, liquid slag
at such temperature.
The carbon of the carbon-containing feed material to be smelted is
combusted in the reactor by the top-submerged injected oxygen-containing
gas. Depending on the carbon content of that material, the combustion may
provide all of the heat requirements of the process. Where the carbon
content is insufficient to meet those requirements, fuel is supplied to
the reactor during the smelting operation, either continuously throughout
the operation, or intermittently. The fuel may comprise at least one of
natural gas, oil or coal. Where the fuel is natural gas, oil or coal
fines, it may be blown into the reactor by the lance providing
top-submerged injection of oxygen for smelting, or by an adjacent lance.
Where the fuel is coal, it may be added to the reactor in a coarse
particulate, or lump form through an inlet chute in an upper region of the
reactor, such as with the carbon-containing feed material.
Iron oxide may be present in the slag, due to the nature of the slag or
slag-forming flux used or as a result of its presence in the
carbon-containing material. Where present in the slag, iron oxide can be
at a level at which it is beneficial in providing an oxygen-carrier from a
location at which oxygen-containing gas is injected into the slag to
carbon of carbon-containing material floating in and reaching to the top
surface of the slag. At that location, FeO.sub.1.5 is able to be formed in
the slag by the reaction:
FeO.sub.(slag) +1/4O.sub.2 =FeO.sub.1.5(slag) (1)
The resultant FeO.sub.1.5 in the slag then is transferred to the
carbon-containing material by turbulence generated by the top-submerged
injection of oxygen-containing gas, so as to combust the carbon C.sub.m
content of particles of the carbon-containing material, by the reaction:
2FeO.sub.1.5(slag) +C.sub.m =2FeO.sub.(slag) +CO (2)
The iron oxide in the slag similarly acts as an oxygen-carrier enhancing
combustion of fuel, if used. Also, CO.sub.2 can also be generated,
depending on the relative abundance of carbon as C.sub.m and in fuel.
Carbon monoxide generated by reaction (2) and the corresponding reaction
involving the combustion of fuel, if used, preferably is post-combusted in
or above the slag. That is, excess air, oxygen or oxygen-enriched air is
provided to achieve substantially complete combustion of the carbon
monoxide to carbon dioxide. Similarly, hydrogen liberated or generated
during smelting, as well as any hydrocarbon gases liberated or generated
by reaction involving any water present, also can be post-combusted.
The oxygen required for post-combustion can be provided by the
top-submerged injected oxygen-containing gas being injected to provide
oxygen in excess of stoichiometric requirements for combustion. Resultant
post-combustion can be at least partially within the slag or above the
slag, depending on the level within the slag at which the
oxygen-containing gas is injected. If required, the top-submerged lance
can have a single jetting nozzle, or a plurality of jetting nozzles, and
in the latter case oxygen for post-combustion can be injected through at
least one nozzle of the lance which is at a divergent angle with respect
to at least one nozzle through which oxygen for combustion is injected.
Alternatively, oxygen for post-combustion can be supplied through a lance
separate from the lance providing oxygen-containing gas for combustion.
The lance supplying post-combustion oxygen may provide for top-blowing, or
it may simply blow oxygen laterally into the reactor space above the slag.
In a further alternative, the oxygen for post-combustion is provided by a
modified form of top-submerged lance, and issues from a shroud of that
lance which terminates above the slag. In this alternative, the shroud is
in the form of an annular sleeve mounted around an upper portion of the
lance to define, between the shroud and the lance, an annular passageway
which is open at its lower end. The supply of oxygen-containing gas to the
passageway, at the upper end of the lance, enables the gas to discharge
into the reactor space, above the slag, to enable required
post-combustion. This arrangement facilitates control over the feed rate
of oxygen for post-combustion independently of top-submerged injection of
oxygen-containing gas for combustion.
Post-combustion has several benefits in the process of the invention. It
enables the release of resultant heat energy to the slag and
carbon-containing feed material, to thereby enhance smelting of the feed
material. Also, it increases the temperature of the reactor off-gases,
increasing the level of heat energy able to be recovered from those gases
without the need for a separate combustion stage. Additionaly, it results
in CO and H.sub.2 of the off-gases being burnt substantially completely to
harmless carbon dioxide and water vapour.
Where the carbon-containing feed material contains fluorides, as is the
case with SPL material, substantially complete removal of fluorine from
the reactor is able to be achieved by the smelting operation. The removal
of fluorine can be enhanced by conducting the smelting in the presence of
a sufficient level of material containing hydrogen compounds which, under
the smelting conditions, form HF which is readily evolved with reactor
off-gases. Hydrogen containing compounds may be present to a sufficient
level in the carbon-containing feed material. However, they additionally
or alternatively may be added to the reactor as water, and/or as fuel
comprising natural gas, oil or coal, with volatiles in the coal providing
such compounds. However, other organic materials can be used, if required.
Slag resulting from the smelting operation, and tapped from the reactor,
can be disposed of or recycled. Where the slag is to be disposed, it can
be cast, but preferably is granulated in a water stream or tank. The slag
can be used as landfill or, where appropriate, it can be used in building
material production. The level of contaminants remaining in the slag
typically is very low and complies with standards set by environmental
agencies for landfill, while the contaminants are substantially
unleachable from the slag by ground-water or the like.
While relatively coarse crushing of carbon-containing feed material to -20
mm generally is sufficient, fines inevitably will be produced. Also, in
the case of aluminium smelter waste able to be smelted with SPL material,
it will be appreciated that spent alumina from dry scrubbers and floor
sweepings, for example, will substantially comprise fines. As indicated
above, fines can be injected through a top-submerged lance. However, fines
feed material preferably is fed to the reactor with sufficient water, or
other suitable binder, to produce a pugged material. This lightly
agglomerated, pugged material can be fed to the reactor through a chute in
an upper region of the reactor, to drop into the slag. The feeding of
fines as pugged material minimises loss of fines from the reactor as dust
carried out through the reactor flue line and, with good practice, less
than 1% of the fine feed is lost.
Water, or an organic or inorganic binder, used to provide pugged fines can
provide the hydrogen compound which facilitates removal of fluorine where,
for example, the carbon-containing material comprises SPL material.
However this water, or water added separately or with carbon-containing
material in a moistened or damp condition, also can be used more generally
to maintain a required heat energy balance in the smelting operation.
Thus, where the fuel value of the carbon and organics content of the
carbon-containing material exceeds the heat requirements of the smelting
operation, the water can be used to maintain the heat balance by taking up
heat energy by volatilization. If required, water for this purpose can be
injected as required, through the or a top-submerged lance or through a
separate pipe.
The slag used or resulting from the process of the invention can have a
significant solubility for all components of commercially available
refractory containment materials. Thus, the life of refractories in the
reactor may be limited, particularly at temperatures in excess of the
preferred upper limit of about 1250.degree. C. The reactor therefore
preferably is provided with water-cooling facilities, such as by forming
the reactor with a double-walled outer metal shell through which coolant
water is circulated. In an alternative arrangement, the reactor has a
single-walled outer metal shell, and supply means located exteriorly of
the shell for spraying coolant water against the outer surface of the
shell. In each case, cooling is provided at least at high-wear areas of
the reactor. The cooling of the reactor by circulated or sprayed coolant
water preferably is such as to form a lining of solidified slag around the
inner, refractory-lined periphery of the reactor, to thereby protect the
refractory from molten slag. Water cooling adds to initial capital cost,
while it also can add to operating costs due to increased heat losses from
the smelting operation. However, the added costs need to be balanced by
lower maintenance costs and increased reactor availability due to less
frequent refractory replacement intervals. Also, the added operating costs
are not significant where the carbon-containing feed material has
sufficient fuel value to avoid the need for fuel addition. The composition
of the slag produced is adjusted by suitable fluxing to ensure the
protective lining of solid slag is obtained at the temperature of
operation.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference now is directed to the accompanying drawings, in which:
FIG. 1 is a schematic representation of a reactor system for use in the
process of the present invention;
FIG. 2 is a process flowsheet illustrating one form of the process of the
present invention; and
FIG. 3 is a process flowsheet illustrating a second form of the process.
The reactor system 10 of FIG. 1 has a furnace reactor 12 in which SPL or
similar or other carbon-containing material is lable to be smelted, and a
top-submerged lance 14 inserted through the roof of reactor 12. A reactor
chamber 16, in which smelting of the SPL material is conducted, is defined
by reactor 12. Chamber 16 is defined within an outer shell 18 of steel
and, internally of shell 18, by a lining of suitable refractory material
19. At least around its lower extent in which charged material and slag is
present during smelting, reactor 12 is adapted for the spraying of coolant
water onto the external surface of shell 18. This is illustrated by
annular water supply conduits 21 which encircle reactor 12 and are
provided with nozzles for generating water jets 23. The spraying of water
is such that resultant cooling of shell 18, and adjacent refractory
material 19, causes a protective skin 20 of solidified slag to be formed;
skin 20 protecting material 19 from dissolution by molten slag.
Carbon-containing material in particulate form, such as SPL material,
typically -20 mm, is fed to chamber 16 via inlet chute 22 in an upper
region of reactor 12. Flux material for slag forming also is charged
through chute 22. While not shown, chute 22 typically will be provided
with appropriate gating means which obviates loss of reactor gases through
chute 22.
Lance 14 has a main conduit means 24 through which top-blown
oxygen-containing gas is supplied by top-submerged injection into chamber
16. Conduit means may comprise a single conduit for that gas, with fumes
of the carbon-containing material and solid fuel fines being entrained in
the gas. Alternatively, conduit means 24 may comprise at least two
concentric conduits, with the gas injected through one of these, with
entrained fines of carbon-containing material if required, and gaseous or
liquid fuel injected through another of the conduits.
In start-up of a smelting operation, lance 24 is lowered in chamber 16 to
an intermediate height, with oxygen-containing gas being blown to generate
a sufficient depth of molten slag 26 to which the carbon-containing
material 28 is added. The intermediate height is such as to cause
splashing of the slag so that slag splashes and is solidified on a lower
extent of conduit means 24. When a sufficient coating 30 of protective
slag has been formed on means 24, lance 14 then is lowered so that its
lower tip-end is in the slag to provide top-submerged, direct injection of
the oxygen-containing gas into the slag.
During smelting, the carbon content of the carbon-containing material, such
as SPL material, and injected fuel is substantially fully combusted,
generating CO.sub.2 and H.sub.2 as reactor off-gases which pass or are
drawn from chamber 16 via flue-offtake 32 of reactor 12. The combustion
liberates fluoride contaminants of the SPL material as HF which is evolved
with other off-gases.
In addition to conduit means 24, lance 14 has a concentric shroud 34 which
is open at its lower end. As shown, the axial extent of shroud 34 from the
upper end of lance 14 is such that, with conduit 24 lowered for
top-submerged injection, the lower end of shroud 34 is spaced above slag
26. Oxygen-containing gas is blown through the annular passage defined
between shroud 34 and conduit means 24, and is discharged into chamber 16
above slag 26 through the open lower end of that passage. The oxygen
content of the gas blown through shroud 34 effects post-combustion of CO
and H.sub.2 to CO.sub.2 and H.sub.2 O in chamber 16, with a substantial
proportion of the heat energy resulting from post-combustion being taken
up by slag 26 and carbon-containing material 28.
From offtake 32, the off-gases pass to a suitable treatment installation.
This may include a dust separator to remove entrained fines. It also may
include a water scrubber for recovery of HF as an aqueous solution, or a
dry scrubber in which the off-gases are contacted with particulate alumina
to form aluminium fluoride.
FIG. 2 is a process flowsheet illustrating the simplicity of the process of
the invention. While self-explanatory in the context of description of
FIG. 1, FIG. 2 highlights that the process can involve only a single stage
smelting operating, requiring only one reactor such as illustrated in FIG.
1.
With reference to FIG. 3, there is shown a flowsheet illustrating operation
in accordance with a second form of the process of the invention. For
this, a single furnace reactor is sufficient, although operation is in a
two-stage, batchwise mode. The process of FIG. 3 is illustrated with
reference to the smelting of carbon-containing material comprising SPL
material. However, as with the process of FIGS. 1 and 2, the process of
FIG. 3 is able to be adapted for similar smelting of other
carbon-containing materials, such as waste graphite blocks from a nuclear
reactor, residue from a vertical retort, graphite material from
metallurgical cupellation crucibles or activated carbon.
In the first stage, a slag heel is provided in the reactor. Feed of SPL
material and flux is progressively charged, while air to combust the free
carbon of the SPL material is injected into the slag by a top-submerged
injecting lance. If necessary fuel and, if required, further air is
injected. Resultant smelting, preferably at from 1100 to 1400.degree. C.,
most preferably at about 1300.degree. C., consumes the carbon content of
the SPL material, while fluorine is extracted with flue gas. Other
contaminants such as H.sub.2 S and HCN are substantially fully destroyed
by combustion with oxygen so that only extremely small amounts leave with
the off-gas. Fluorine typically is extracted as HF vapour which is able to
be recovered for reuse. However, some fluorine can report in the flue gas
as NaF fume and, where this is the case, the fume preferably is recycled
to the first stage operation. This recycling of NaF fume enables increased
exposure to the furnace reaction conditions, enabling reaction of the NaF
to generate further HF, with the sodium being taken up by the slag.
On completion of the first stage, the feeding of SPL material and flux is
terminated. The slag then is subjected to a blow down period at a similar
temperature to that used in the first stage, with ongoing top-submerged
injection of air and fuel. Combustion of the fuel and residual SPL
material is continued, at least until the latter is exhausted and the flue
gas is substantially free of HF. Any NaF present in the second stage flue
gas can be recycled to the furnace in that stage, as shown for the first
stage. After the second stage, there then remains a slag which, after
granulation in a stream of water, can be discarded or used as
environmentally acceptable land fill low in toxic elements such as
fluorine and HCN. A residual heel of slag is retained, for commencement of
a further two-stage cycle of operation.
The invention now will be further illustrated by reference to the following
specific Examples.
EXAMPLE 1
300 kg of Cut 1 SPL and 200 kg of Cut 2 SPL material together with 320 kg
of flux slag were fed over a period of 280 minutes into a liquid bath
comprising 100 kg of flux slag containing iron oxide held at temperatures
of 1255 to 1300.degree. C. in a top submerged lancing furnace. The mix of
feed had been crushed to minus 20 mm sizing and was mixed with 10% water
by weight of SPL just prior to entering the feed port in the top of the
furnace. The Cut 1, Cut 2 and flux slag had compositions as shown in Table
1.
TABLE 1
______________________________________
ASSAY OF MATERIALS - EXAMPLE 1
Fe SiO.sub.2
Al.sub.2 O.sub.3
CaO MgO C F Na
% % % % % % % %
______________________________________
SPL Cut 1
3.3 14.4 26.9 2.1 1.3 10.0 6.8 19.8
SPL Cut 2 3.7 10.0 29.0 3.0 1.2 2.4 7.2 21.8
Flux Slag 21.4 16.1 6.9 32.9 3.5 -- 0.4 0.1
Final Slag 17.8 20.5 17.8 15.7 4.8 -- 0.6 9.0
______________________________________
The top submerged lance was fired with natural gas at a rate of 40 Nm.sup.3
/h. Air and oxygen were injected with the natural gas to completely burn
the natural gas as well as the carbon in the SPL. The air was enriched
with the oxygen for a total of 23% oxygen. The post-combustion air was
injected at a rate of 75 Nm.sup.3 /h above the bath, using a shroud system
which forms part of the lance.
During the smelting operation and at the end of the smelting period slag
was tapped from the furnace after allowing a digestion period of ten
minutes to digest the last of the feed.
The final slag was granulated in water and had an assay as shown above. A
leaching test specified by the EPA in Victoria was carried out on the
final slag. The solution contained 7.2 mg/l fluoride ion, which was well
within the requirements for material for landfill of less than 150 mg/l.
The pilot plant facilities were provided with a hygiene ducting and
baghouse system to ensure a safe and clean working environment. The gas
handling system from the furnace contained a cooler, baghouse and sodium
carbonate scrubbing towers. Environmental monitoring was performed on both
the flue gas system and the hygiene scrubbing system, as well as in the
working environment. The tests indicated compliance of the plant for the
levels in the gas emissions of particulate matter, nitrogen oxides,
sulphur trioxide, sulphur dioxide, carbon monoxide, hydrogen fluoride,
hydrogen sulphide, phosgene, methane and ammonia. The work place
environment had undetectable levels of all pollutants during plant
operations. The carbon content in the feed was completely burnt to
CO.sub.2 in the operations and the tapped slag contained no carbon.
Approximately 90% of the fluorine in the SPL feed was removed as HF and
collected in the scrubber system. Less than 1% of the weight of SPL was
collected as fume and dust in both baghouses. The baghouse fume contained
20.3% F and 22.0% Na, indicating that it contained mostly NaF. This
represented 1.5% of the total fluorine in SPL feeds.
EXAMPLE 2
A plant has been designed to process in a top submerged lancing reactor as
in FIG. 1, operating at 1300.degree. C., 20,000 tpa of SPL assay shown in
Table 2.
TABLE 2
______________________________________
ASSAY OF MATERIALS - EXAMPLE 2
Fe SiO.sub.2
Al.sub.2 O.sub.3
CaO MgO C F Na
% % % % % % % %
______________________________________
SPL Cut 1
1.6 2.1 5.0 -- -- 67.6 12.9 7.8
SPL Cut 2 1.6 36.0 15.7 -- -- 5.0 17.1 10.4
Flux Slag 21.3 16.1 16.6 33.8 4.8 -- -- 0.1
Final Slag 14.5 24.6 12.2 21.3 9.2 -- 0.7 7.6
______________________________________
The plant uses a heel of 974 kg of discard slag as the starting bath for a
cycle of smelting SPL Cut 1 and Cut 2 at 2.1 tonne/h and 1.4 tonne/h
respectively. The iron oxide containing flux slag is smelted at 2.4
tonne/h while firing the top submerged lance with 100 Nm.sup.3 /h of
natural gas, 960 Nm.sup.3 /h of combustion air, 13,400 Nm.sup.3 /h of
smelting air and 2,000 Nm.sup.3 /h of afterburn air. The furnace capacity
is reached after 4.15 hours of smelting and feeding of all materials is
stopped and firing is changed to provide the heat needed to maintain the
temperature at 1300.degree. C. whilst digesting the last of the feed over
a period of 15 minutes. Following this the slag is tapped from the furnace
into a granulation launder for discard or sale, leaving a heal of slag in
the furnace for the bath needed for the next cycle of scrubbing.
The flue gases are cooled and ducted to a scrubbing system to collect the
HF in a reuseable form.
As in Example 1 the slag is suitable for use as landfill or for other
purposes.
In the preceding description, reference is to substantially complete
post-combustion. This is to ensure that evolved contaminants such as HCN
are fully combusted to harmless gases. However, it is to be understood
that less than complete post-combustion is possible, with full combustion
being effected externally of the reactor in a suitable after-burner
device, if required.
EXAMPLE 3
A sample of vertical retort residue material, obtained following
distillation of zinc from zinc concentrate mixed with coke, was subjected
to laboratory scale top-submerged lance smelting. The conditions used were
comparable to those described with reference to FIGS. 1 and 2 for SPL
material. The composition of the residue was as shown in Table 3.
TABLE 3
______________________________________
RESIDUE ANALYSIS - EXAMPLE 3
Constituent
______________________________________
Zn 3.6 wt %
Pb 4.9 wt %
Fe 11.2 wt %
SiO.sub.2 18.3 wt
CaO 4.8 wt %
S 2.2 wt %
AS 0.6 wt %
Al.sub.2 O.sub.3 6.1 wt %
C 32.2 wt %
Aq 115 ppm
______________________________________
For smelting the residue, a start-up bath of reverberatory slag initially
was melted and heated to the required operating temperature of
1350.degree. C. The composition of the slag is shown in Table 4.
TABLE 4
______________________________________
SLAG COMPOSITION - EXAMPLE 3
Constituent
Wt %
______________________________________
Fe 37.1
Fe.sub.2 O.sub.3 4.9
SiO.sub.2 36.8
CaO 9.5
Al.sub.2 O.sub.3 3.7
Zn 0.09
Pb 0.02
Cu 0.46
S 0.97
______________________________________
The residue was fed progressively to the molten slag, together with flux.
The flux was limestone containing 45.8 wt % CaO and 4.1 wt % SiO.sub.2.
While smelting was essentially in accordance with FIG. 2, it was on a
laboratory scale in simulating equipment, rather than in a furnace reactor
as in FIG. 1. The smelting was conducted in a covered alumino-silicate
crucible which was provided with initial and supplemental heating in an
induction furnace. Air was injected into the slag bath, using a 1.5 mm
internal diameter alumina tube, at a controlled rate simulating top
submerged lance smelting. A nitrogen cover gas was injected into the space
above the bath, to prevent air ingress. Weighed quantities of residue and
flux were added to the crucible at one minute intervals; the overall feed
rate equivalent to 5 g/min of residue feed equivalent. The bath
temperature was measured by a thermocouple protected by an
alumino-silicate sheath and immersed in the bath. The temperature was
controlled manually, by adjustment of power to the induction furnace.
The overall smelting parameters, starting with 100 g of slag, and injection
of nitrogen into the slag for 5 minutes before the supply of residue and
flux, and switching to top-submerged injection of air, are set out in
Table 5.
TABLE 5
______________________________________
SMELTING PARAMETERS
Conditions of Smelting
75% oxidation
______________________________________
Feed
Residue 200 g
Flux 20 g
Injection Rate
Air 4.77 1/min
Temperature 1350.degree. C.
Time 60 min
______________________________________
The results of smelting are set out in Table 6.
TABLE 6
______________________________________
SMELTING RESULTS
Products Wt %/ppm
______________________________________
Final slag (231 g)
Zn 0.59%
Pb 0.41%
S 0.05%
Fe 46.2%
Ag 20 ppm
Fume (10.2 g)
Zn 20.90%
Pb 42.40%
S 3.70%
Fe 1.60%
Ag 305 ppm
Ash (7.2 g)
Zn 0.82%
Pb 0.52%
S 5.01%
Fe 11.20%
Ag 200 ppm
______________________________________
The results show that vertical retort residue can be smelted in accordance
with the present invention. The smelting enables carbon in the residue to
be utilised as a fuel and reductant. Also, recovery of more than 90% of
the zinc and lead content, as clean fume, is able to be achieved.
EXAMPLE 4
A range of trials, similar to Example 3, was conducted with vertical retort
residue. In these trials, air flow rates varied from 0% to 100% of the
carbon content of the residue based on the analysis of Table 3, compared
with the 75% oxidation level in Example 3. In a trial with no oxidation
and no flux used, but with injection of nitrogen, an incompletely molten
product was obtained, leaving large quantities of ash (about 84 g). That
trial did not allow adequate mixing and reaction in the bath, and high
levels of zinc and lead were left in the ash. In another trial using
oxygen injection for oxidation of 25%, with only 75% of the limestone flux
level of Example 3, ash weight decreased to 23 g but, again, mixing still
was unsatisfactory, as was zinc and lead recovery (there being over 1 wt %
of each in the slag).
Trials with oxygen injection for 50 to 90% oxidation produced slag with
well below 1.0 wt % zinc and lead. One trial, at 50% oxidation, achieved
the lowest levels of zinc and lead in the slag, but, at such levels, a
speiss phase was present and, more importantly, a large quantity of ash
(58.4 g) was left on the slag. Increasing the oxidation rate to 75%, as in
Example 3, reduced the amount of ash to about 10.8 g while maintaining the
levels of zinc and lead in the slag around 0.5%. Those levels were
maintained in trials operated at oxidation rates of 90%, with ash levels
being further suppressed to about 8 g.
Trials aimed at combusting 100% of the carbon content of the residue
utilised a first smelting stage and a second reduction stage. The smelting
stage was run for 90 minutes, but otherwise was in accordance with Example
3. The reduction stage was for 30 minutes, during which coal as reductant
was added at 0.5 g/min. While the level of lead in the resultant slag was
well below 1%, the level of zinc was at about 1%. This is not typical of
zinc reduction from slag and is believed to be due to preferential
reduction of magnetite before zinc fuming can occur, suggesting the need
for a longer reduction time. However, use of a gaseous reductant such as
natural gas was found to be more efficient than coal and can offset this
effect.
Further single stage trials used carbon in the feed material to act as a
reductant. This was found to be beneficial and, subject to oxidation rate,
enable high recovery of lead and zinc with well below 1% zinc and below
0.5% lead in the slag. In still further trials, increasing the level of
flux addition did not effect the removal of zinc and lead from the slag,
but it did however further decrease the amount of ash remaining after
smelting.
In general, in the further trials of Example 4, and in Example 3, arsenic,
antimony and silver were substantially removed from the residue during
smelting. In the case of arsenic, usually recovered as fume, its level was
reduced from an initial value of 6000 ppm in the residue to 300 ppm in the
slag. Removal of arsenic was enhanced if a speiss phase formed. Of the
order of 50% recovery of arsenic generally was effected as fume. With use
of natural gas as a reductant, and a speiss phase formed, up to 95%
recovery of arsenic in the speiss was possible.
Silver was removed to fume from 115 ppm in the residue feed to about 10 to
20 ppm in slag under smelting conditions achieving successful removal of
zinc and lead. The inferred recovery of silver to fume (and speiss where
applicable) ranged from 80 to 90%.
Fume samples typically contained 25% Zn, 40% Pb, 1% Fe, 0.5% CaO, 2.6% S,
3.5% As, 3.3% C, 1.0% SiO.sub.2, 0.2% Cu, 0.1% Al.sub.2 O.sub.3, 0.25% Sb
and 240 ppm Ag. Carbon levels of less than 1% were obtained in some
trials.
A speiss phase was produced at 1300.degree. C. with oxidation rates between
50% and 75%. A typical speiss contained 0.13% Zn, 0.34% Pb, 70.3% Fe,
4.75% S and 7.3% Cu. Increasing temperature and/or the percentage
oxidation of carbon in the residue decreased the likelihood of speiss
formation. Use of natural gas feed as reductant during smelting produced a
speiss phase; the speiss tending to be lower in zinc and lead but also
containing about 4% As.
The amount of ash formed was dependant on smelting temperature, oxidation
rate and the flux rate. An increase in each of these parameters decreased
the amount of ash. The ash consisted of unreacted residue feed material.
In general, when the ash was completely or substantially completely
removed, the zinc in slag was greater than 0.5% and the lead level also
was higher. A typical analysis range for the ash is set out in Table 7.
TABLE 7
______________________________________
ASH ANALYSIS
Constituent Low High
______________________________________
Fe 4.60% 15.60%
C 0.66% 70.00%
SiO.sub.2 2.36% 35.00%
CaO 1.10% 14.80%
Al.sub.2 O.sub.3 3.70% 7.62%
Zn 0.19% 1.65%
Pb 0.06% 2.06%
Cu 0.38% 6.45%
S 1.80% 12.10%
As 0.12% 0.90%
Aq 20 ppm 200 ppm
Sb 100 ppm 1000 ppm
______________________________________
With reference to Examples 1 to 4 and the preceding description, it will be
appreciated from Example 4, in particular, that the present invention can
be operated in the presence of a metal phase. Indeed, it is to be
understood that the smelting operation of the present invention can form
part of a process for the recovery of metal values from a suitable ore,
concentrate or the like, or for the recovery of metal values from an
intermediate or discard material such as a slag. That is, the
carbon-containing material to be smelted by the process of the present
invention can be used, in effect, as a fuel and/or reductant enabling
recovery of metal values from another material or product. In general,
this use of the invention will not be practical, due to limited
availability of the respective materials at a common site. Also, of
course, there is a need for a suitable degree of compatibility between the
carbon-containing material, and a metal value containing material or
product. Thus, while it can be acceptable to smelt a vertical retort
residue, using a zinc containing slag, for recovery of zinc fume from each
material, it clearly would be undesirable to use a radioactive
carbon-containing material in such context. However, notwithstanding such
ability to use the carbon-containing material to aid in recovery of metal
values from another material, it generally is appropriate for the present
invention to be used solely for smelting the carbon-containing material
alone.
Finally, it is to be understood that various alterations, modifications
and/or additions may be introduced into the constructions and arrangements
of parts previously described without departing from the spirit or ambit
of the invention.
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